Conventional Total Air Temperature (TAT) probes, although often remarkably efficient as a TAT sensor, sometimes face the difficulty of working in icing conditions. During flight in icing conditions, water droplets, and/or ice crystals, are ingested into the TAT probe where, under moderate to severe conditions, they can accrete on the TAT probe surfaces. If operation in the severe weather persists, internal accretion may lead to congestion and clogging around the internal sensing element. Further, internal TAT congestion may lead to a temporary erroneous TAT reading. To address this problem, conventional TAT probes may be electrically heated and also incorporate an elbow, or bend, to inertially separate particles in airflow before reaching the sensing element. FIG. 1 illustrates a typical TAT probe design with an inclined surface upstream of the element passage commonly referred to as an air bump. The air bump aids inertial filtering and also provides a means of boundary layer bleed control. The air bump provides a significant projected area that will be exposed to particle impacts. Particle impacts on the heated air bump may produce surface liquid that may limit satisfactory performance in rain, ice and ice crystal environments.
Another phenomena which presents difficulties to some conventional TAT probe designs has to do with the problem of boundary layer separation, or “spillage”, at low mass flows. Flow separation creates two problems for the accurate measurement of TAT. The first has to do with turbulence and the creation of irrecoverable losses that reduce the measured value of TAT. The second is tied to the necessity of having to heat the probe in order to prevent ice formation during icing conditions. Anti-icing performance is facilitated by heater elements embedded in the housing walls. Unfortunately, probe surface heating also heats the internal boundary layers of air which, if not properly controlled, provide an extraneous heat source in the measurement of TAT. This type of error, commonly referred to as DHE (Deicing Heater Error), may contribute to uncorrectable temperature error. The internal temperature element is typically thermally isolated from the main heated probe so that DHE is minimized. Under certain icing conditions internal accretion may form and grow on the thermally isolated temperature element. Rapid, and sometimes complete, blockage of the probe may occur, thereby leading to erroneous temperature measurements. Introduction of more severe aerospace icing requirements are increasingly problematic for conventional TAT probes.